Catalytic oxidation of alkyl substituted aromatic compounds



Patented June 10, 1%41 CATALYTIC OXIDATION OF ALKYL SUBSTI- TUTEDAROMATIC COMPOUNDS Donald J. Loder, Wilmington, Del., assignor to E. I.du Pont de Nemours & Company, WilminI- ton, DeL, a corporation ofDelaware No Drawing. Application October 1a. 1938, Serial No. 235,578

Claims.

This invention relates to oxidation of alkylsubstituted aromaticcompounds and, more particularly to the production of aromatic acids byoxidation of alkyl-substituted aromatic hydrocarbons.

It is an object of the present invention to provide a process for thecontrolled oxidation of alkyl-substituted aromatic compounds,particularly toluene, xylene and the substituted benzenes.

It is a further and more specific object of the present invention toprovide a new and improved process for the production, fromalkyl-substituted aromatic compounds, of aromatic acids without ruptureof the aromatic ring, and more particularly to obtain benzoic acid fromtoluene, toluic and phthalic acids from xylene, and benzene mono orpolycarboxylic acids and alkyl-substituted derivatives from thecorresponding alkylsubstituted benzenes.

Other objects and advantages of the present invention will be apparentby reference to the following specification.

I have found that oxidation without ring cleavage of alkyl-substitutedaromatic compounds with production in good yield of the correspondingacids can be accomplished by subjecting the said compounds to oxidationin the liquid phase by means of an oxygen-containing gas, for exampleoxygen or air or air enriched with oxygen.

In this manner it is possible to oxidize hydrocarbons, such as toluene,xylene and other alkylsubstituted benzenes with production of benzoic,toluic and phthalic acids or other benzene monoor polycarboxylic acidsand alkyl-substltuted derivatives thereof. Similarly alkyl-substitutedaromatic compounds which contain substituents, in addition to alkylgroups may also be oxidized ac cording to this invention, such forexample as alkyl-substituted aromatic compounds containing N02, halogen,and carboxyl groups. While my process may be carried out at varioustemperatures ranging upward from about 100 C. to about 320 0., generallyspeaking the use of temperatures in the more restricted range of 130-2500., tends, other conditions remaining the same, to give less of partialoxidation products, less loss of carbon to oxides of carbon, and ahigher proportion of acids.

I have further discovered three factors which, all taken together,produce the optimum result but which, nevertheless, individuallycontribute to an improved result as will appear hereinafter. Each ofthese factors, or methods, facilitate oxidation at low temperatures,improved results are obtained when any two of them are employed and thebest results are secured when all three methods are used simultaneously.

As one of the three factors previously mentioried, I have found that theyields of acid produced according to my invention may be considerablyincreased by carrying on the oxidation in the presence of an oxidationcatalyst, such, specifically as the solid polyvalent metals having anatomic weight between about and about 200. For example, I may use suchmetals in the finely divided metallic state or asorganic and inorganicsalts or oxides including such specific metals as cerium, cobalt,copper, manganese, and uranium, with or without inorganic acids such asnitric, phosphoric and hydrochloric acids or mixtures of any two or moreof these substances, As specific catalysts under the above descriptionthere may be employed vanadium, cerium and cobalt chlorides, manganeseacetate alone or together with barium acetate, barium or cobaltpermanganate, sodium cobalti nitrite or mixtures of two or more of suchcompounds, In addition to the oxidation catalysts, promoters such as thealkali and alkaline earth metals may also be employed, if desired, such,for example as the barium, magnesium and potassium acetates, butyrates,propionates, and the like.

I have also found that enhanced yields of arcmatic acids are obtained ifthe oxidation is carried on in the presence of a solvent for thehydrocarbons. Various liquids substantially inert to the oxidation andcapable of dissolving the hydrocarbons such as carbon tetrachloride andbenzene can be used, but I prefer to use as solvent an organic acid,such as acetic, propionic, butyric, trimethyl acetic and isobutyric,such aromatic acids as phenyl acetic, and such hydroxy acids orderivatives as methoxy acetic, and the like. Varying proportions ofthese acids, based upon the weight per cent. present in the solutionbeing oxidized, may be utilized, such as from 1 to 99 per cent. byweight "although I prefer to utilize about 10 to 50 per cent. Withinthese indicated ranges I have found that the solvents eifect aconsiderable increase in the yield, of aromatic acid obtained byoxidation of the hydrocarbon.

As a further feature of the invention I have found that, especially whenoperating at the lower temperatures, say 200 or below, the yields andefilciency of the process may be even further improved by carrying onthe oxidation, whether with or without the solvents referred to, in thepresence of one or more initiators, which term I employ herein todesignate substances capable of initiating attack on the hydrocarbonmolecule which may itself not readily react with molecular oxygen undermy preferred low temperature conditions. Forexample, there may beemployed or- 'ganic peroxides such as benzoyl peroxide; inorganicperoxides: peracids, such as peracetic and perbenzoic acids; thealdehydes, such as acetaldehyde, propionaldehyde, and isobutyraldehyde;ketones, such as acetone, methyl ethyl ketone, diethyl ketone, andcyclohexanone; ethers, such as diisopropyl, diethyl and diamyl ethers;olefines such as cyclohexene and octylene, and, in fact, any organiccompound which tends to form peroxide bodies under the reactionconditions.

The initiator may be added to the reactants at the start or continuouslyduring the oxidation or both; or, if preferred the oxidation may bebegun at a temperature and pressure at which partial oxidation products,capable of being oxidized to or acting as oxygen carriers are formed,and the partially oxidized hydrocarbons thus produced may thereafter actas oxygen carriers capable of attacking other hydrocarbon molecules atthe relatively low temperatures which I have generally outlined and willhereinafter more specifically describe. The constant maintenance of aconcentration of initiator is important, however, and therefore, ingeneral, I deliberately add the initiator to the reactants as describedhereinafter. The oxygen carrier is thus able to initiate the oxidationwhich then may become at least partially self-sustaining at temperaturesvery much lower than otherwise possible.

The proportions of initiators which are desirable according to thisinvention range from about 0.1 to per cent, based upon the weight of thehydrocarbon being treated. I do not wish to be restricted to theseproportions, however, for I have found that as much as 50 per centinitiator may be utilized without deleterious effect upon progress ofthe oxidation and at the same time as low as 0.05 per cent initiator maybe employed with an increased eillciency and yield of aromatic acid.Although primarily applicable to ketones such as acetone, dimethyl ormethyl ethyl ketones, or cyclohexanone, or mixtures thereof, theseranges describe satisfactorily the amounts of other initiators which aresuitable according to my invention.

While the process is operable at ordinary pressures I prefer to useelevated pressures rangingupwards from about 2 atmospheres to about 100atmospheres. Although pressures in the neighborhood of from 10 to 50atmospheres are: preferred, higher pressures, for example as high as1000 atmospheres, may be used. The minimum pressure is that required topermit effecting the reaction in the liquid phase, by which is meantthat the hydrocarbon is preferably oxidized in the liquid or dissolvedstate. Pressures in excess of this minimum may be used, however, sincepressure has been found to favor the reaction rate.

Having described separately some of the features of my invention, thefollowing examples will illustrate how these features may be combinedfor oxidation of alkyl-substituted aromatic compounds generally.

Example 1.--A mixture containing 276 grams toluene, 276 grams aceticacid, 0.23 grams cobalt acetate, 0.23 grams manganesipcetate and 4.3grams methylethyl tantalum lined converter of 1200 cc. capacity,provided with suitably valved gas outlet and inlet lines at top andbottom, respectively. The

ketone wascharged into av acetophenone.

mixture was heated to 190 C., under a pressure of 50 atmospheres and airwas bubbled through the mixture for 3 hours at the rate of 200 litersper hour, the pressure being maintained at 50 atmospheres and thetemperature at 185-200 C. The exit gas was directed through a condenser,and traps cooled by dry ice. Solid benzoic acid was removed from theoxidation products and recovered by cooling the final product tocrystallize the benzoic acid. The total.

weight of benzoic acid recovered was 126.9 grams. An additional 45.8grams of benzoic acid was recovered from the filtrate after strippingof! the acetic acid and unconverted toluene. 123.2 grams of unusedtoluene was recovered. The conversion and yield were 47.2% and 85.2%respectively. The residue obtained after recovery of benzoic and aceticacids consisted of henzaldehyde and tar.

Example 2.A mixture containing 425.0 grams ethyl benzene, 63.1 gramsacetic acid, and 0.05 grams cobalt acetate was charged into atantalum-lined converter of v1200 cc. capacity, provided with suitablyvalved outlet and inlet lines at top and bottom, respectively. Themixture was heated to 168-178" C. for 1% hours under a pressure of 50atmospheres. Air was bubbled through the mixture for 1% hours at therate of 225 liters per hour, the pressure being maintained at 50atmospheres and the temperature at 'l68-178 C. The exit gas was directedthrough a condenser, and traps cooled by dry ice.

Solid benzoic acid was removed from the oxidation product and recoveredby cooling the final products to' crystallize the benzoic acid. Thetotal weight of benzoic acid recovered was 24.1 grams. In addition,there was separated from the final product 2.8 grams phenyl ethyl ester,1.1 grams phenyl ethanol, and 53.6 grams 122.2 grams of unreacted ethylbenzene was recovered. The conversion and yield to benzoic acid were,respectively, 18.2% and 25.6%. The conversion and yield to acetophenonewere, respectively, 41.4% and 58%.

Example 3.-Into a tantalum-lined converter, such as described inExamples 1 and 2, was charged 236.0 grams of mixed xylenes, 130.6 gramsacetic acid, 3.7 grams diethyl ketone, 0.185 grams cobalt acetate and0.185 grams manganese acetate. This mixture was heated to 187-202 C.under a pressure of 50 atmospheres and air was bubbled through themixture at this temperature and pressure for 2 hours at the rate of 250liters per hour.

By distillation under atmospheric and reduced pressures, the reactionproducts were separated to give 75.7 grams of unreacted xylenes, and50.3% yield of toluic acids, 2.0% yield of phthalic acids, 1.5% yield oftoluyl alcohols, 8.1% yield of toluyl esters and 5.7% yield of toluicaldehydes.

Example 4.--Into a converter such as described in Examples 1 and 2 therewas charged a mixture containing 400 grams isopropyl benzene, 4 gramswater and 0.4 gram cobalt acetate. This mixture was heated at atemperature of 170-229" C. under a pressure of 30 atmospheres and airwas bubbled through this-mixture for 2 hours at the rate of 250 litersper hour. At the expiration of this time the reaction products wereseparated by distillation to give 45 grams benzoic acid, and 230 gramscumene. The remaining material was of a tarry nature. The yield ofbenzoic acid was about 35%.

Although specific disclosure has been made in the examples of methodsfor carrying on my invention in a batch process, it should be understoodthat this invention may also be practiced in a continuous manner. Thus,after completion of the benzoic acid or other acid production, such asshown in the specific examples, the materials capable of being convertedto the desired acid, plus the catalyst, solvent, and initiator may berecovered and recycled to the reaction zone together with furtherquantities of aromatic hydrocarbon. In a continuous process it will alsobe found desirable to make such additions of catalyst, solvent, andinitiator as will maintain the reaction rate and yield of acid at thedesired high degree.

While the process as described in the examples involves passage of theoxidizing gas through a body of liquid, it will be understood that othermeans of assuring the desired liquid-gas contact may be employed, as,for example, passage or liquid and gas co-current or counter-currentthrough a tube or tower, which may be supplied with plates, packing orother devices for enhancing contact.

I claim:

1. A method of oxidizing aromatic compounds containing alkvlsubstituents which comprises subjecting such compounds to oxidation inthe liquid phase by means of a gas containing gaseous oxygen in thepresence of an oxidation catalyst and a solvent for the aromaticcompound which is substantially inert to the oxidation.

2. A method of oxidizing aromatic compounds containing alkylsubstituents which comprises subjecting such compounds to oxidation bymeans of a gas containing gaseous oxygen in the presence of an oxidationcatalyst, an oxidation initiator selected from the group consisting ofperoxides and compounds which form peroxides under the reactionconditions and a solvent for the aromatic compound which issubstantially inert to the oxidation at a temperature in the range of100-320 C. and at a pressure in the range of 2 to 1000 atmospheres andseparating the corresponding aromatic acid from the reaction mixture.

3. A method of oxidizing aromatic compounds containing alkylsubstituents which comprises subjecting such compounds to oxidation inthe liquid phase by means of a gas containing gaseous oxygen in thepresence of an oxidation catalyst, an oxidation initiator. selected fromthe group consisting of peroxides and compounds which form peroxidesunder the reaction conditions and a solvent for the aromatic compoundwhich is substantially inert to the oxidation at r a temperature in therange of lO-320 C. and at a pressure in the range of 2 to 1000atmospheres and separating the corresponding aromatic acid from thereaction mixture.

4. A method of oxidizing aromatic compounds containing alkylsubstituents which comprises subjecting such compounds to oxidation inthe liquid phase by means of a gas containing gase ous oxygen in thepresence of an oxidation catalyst, an oxidation initiator selected fromthe group consisting of peroxides and compounds which form peroxidesunder the reaction conditions and a solvent for the aromatic compoundwhich is substantially inert to the oxidation at a temperature in therange of 130-250 C. and at a pressure in the range of 2 to 100atmospheres and separating the corresponding aromatic acid from thereaction mixture.

5. A method of producing aromatic acids which comprises subjecting analkyl substituted aromatic compound to oxidation by means of a gascontaining gaseous oxygen in the presence of an oxidation catalyst, anoxidation initiator selected from the group consisting of peroxides andcompounds which form peroxides under the reaction conditions andasolvent for the aromatic compound which is substantially inert to theoxidation at a temperature in the range of -320 C. and at a pressure inthe range of 2 to 1000 atmospheres and separating the correspondingaromatic acid from the reaction mixture.

6. A method of producing aromatic acids which comprises subjecting analkyl substituted aromatic compound to oxidation in the liquid phase bymeans of a gas containing gaseous oxygen in the presence of an oxidationcatalyst, an oxidation initiator selected from the group consisting ofperoxides and compounds which form peroxides under the reactionconditions and a solvent for the aromatic compound which issubstantially inert to the oxidation at a temperature in the range of100-320 C. and at a pressure in the range of 2 to 1000 atmospheres andseparating the corresponding aromatic acid from the reaction mixture.

7. A method of producing aromatic acids which comprises subjecting analkyl substituted aromatic compound to oxidation in the liquid phase bymeans of a gas containing gaseous oxygen in the presence of an oxidationcatalyst, an oxidation initiator selected from the group consisting ofperoxides and compounds which form peroxides under the reactionconditions and a solvent for the aromatic compound which issubstantially inert to the oxidation at a temperature in the range of-250 C. and at a pressure in the range of 2 to 1000 atmospheres andseparating the corresponding aromatic acid from the reaction mixture.

8. A method of producing benzoic acid which comprises subjecting tolueneto oxidation by means of a gas containing gaseous oxygen in the presenceof an oxidation catalyst and a solvent for the toluene" which issubstantially inert to the oxidation.

9. A method of producing benzoic acid which comprises subjecting tolueneto oxidation in the liquid phase by means of a gas containing gaseousoxygen in the presence of an oxidation catalyst and a solvent for thetoluene which is substantially inert to the oxidation.

10. A method of producing benzoic acid which comprises subjectingtoluene to oxidation by means 01' a gas containing gaseous oxygen in thepresence of an oxidation catalyst, an oxidation initiator selected fromthe group consisting of peroxides and compounds which form peroxidesunder the reaction conditions, and a solvent for the toluene which issubstantially inert to the oxidation at a temperature in the range ofl00-320 C. and at a pressure in the range of 2 to 1000 atmospheres andseparating the benzoic acid from the reaction mixture.

11. A method of producing benzoic acid which comprises subjectingtoluene to oxidation in the liquid phase by means of a gas containinggaseous oxygen in the presence of an oxidation catalyst, an oxidationinitiator selected from the group consisting of peroxides and compoundswhich form peroxides under the reaction conditions, and a solvent forthe toluene which is substantially inert to the oxidation at atemperature in the range of l00320 C. and at a pressure in the range of2 to 1000 atmospheres,

and separating the benzoic acid from the reaction mixture.

12. A method of producing benzoic acid which comprises subjectingtoluene to oxidation in the liquid phase by means of a gas containinggaseous oxygen in the presence of an oxidation catalyst, an oxidationinitiator selected from the group consisting of peroxides and compoundswhich ,form peroxides under the reaction conditions, and a solvent forthe toluene which is substantially inert to the oxidation at atemperature in the range of 130-250 C., and at a pressure in the rangeof 2 to 100 atmospheres, and separating the benzoic acid from thereaction mixture.

13. A method of producing benzoic acid which comprises subjectingtoluene to oxidation in the liquid phase by means of a gas containinggaseous oxygen in the presence of a cobalt acetate catalyst, an aceticacid'solvent, and an oxidation initiator selected from the groupconsisting oi! peroxides and compounds which form peroxides under thereaction conditions, at a temperature in the range of 100-320 0., and ata pressure in the range of 2 to 100 atmospheres, and separating thebenzoic acid from the reaction mixture.

14. A method of producing benzoic acid which comprises subjectingtoluene to oxidation in the liquid phase by means of a gas containinggaseous oxygen in the presence of a cobalt acetate catalyst, an aceticacid solvent, and an oxidation initiator selected from the groupconsisting of peroxides and compounds which form peroxides under thereaction conditions, at a temperature in the range of 130-250 C.', andat a pressure in the range of 2 to 1000 atmospheres, and separating thebenzoic acid from the reaction mixture.

15. A method of producing benzoic acid which comprises subjectingtoluene to oxidation in the liquid phase by means of a gas containinggaseous oxygen in the presence of an oxidation catalyst, an oxidationinitiator selected from the group consisting of peroxides and compoundswhich form peroxides under the reaction conditions, and a loweraliphatic acid solvent for the toluene at a temperature in the range of130- 250 C., and at a pressure in the range of 2 to 100 atmospheres, andseparating the benzoic acid from the reaction mixture.

DONALD J. LODER.

CERTIFICATE OF CORRECTION.

Patent No.2; 214.5,528. June 10, 19in.

' DONALD J. LODER.

It is hereby certified that error appears in the printed specificationof the above numbered pstent requiring correction as follows: Page 11.;first column, line 25, claim 15, for "2 to 100" read --2 to 1000"; andsecon'd column, 11m 10, claim 1A, for "2 to 1000" read --2 to 1oo--; andthat are said Letters Patent should be read with this correction thereinthat the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 15th day of July, A. 4). 191m.

Henry Van Arsdale,

Acting Commissioner of Patents. (Seal)

